This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Hyperpolarized gas MR imaging in small animals (and other studies as well) have generally required a dedicated ventilator system. The use of expensive rare isotopes (such as 3He and 129Xe) present a need to miinimize cost by recycling these gases after they have been used for imaging.